Even with the Islamic State on the run, U.S. advisers grapple with political and military problems in wresting Iraqi and Syrian towns from extremists.
The shuttering of the C.I.A. program, one of the most expensive efforts to arm and train rebels since the 1980s, has forced a reckoning over its successes and failures.
Risky Special Operations missions targeting midlevel figures can prove valuable for unearthing information about the Islamic State’s inner circle.
The drone had dropped a munition near Syrian fighters who were accompanied by advisers from the American-led coalition, the United States military said.
Defense Secretary Jim Mattis said President Trump’s decision to give the military more latitude had put greater pressure on militants in Syria, Yemen and Somalia.
In a pointed departure from one of President Trump’s bedrock populist positions, Ms. Trump said the United States might need to admit more refugees.